Wide band high-frequency transmission line



June 14, 1949. M. w. scHELDoRF I 2,473,262

WIDE BAND HIGH-FREQUENCY TRANSMISSION LINE Filed Nov. l, 1945 In Venter: Marve l W Sc: n e Iciorf,

,OZ/.wm l-Iie Attorney.

Patented June 14, 1949 WIDEBAN D HIGHLFREQUENCY TRANSMISSION LINE Marvel W. Scheldorf, Schenectady, N; Y.,assignr:' to General Electric Company, a,corporationa0f.A

New York Application November 1, 1945', Serial No.- 62'6g137 4 Claims. (Cl. 178-44.)

My -invention relates toY a. high frequency transmissioni'meand it. has forits primary object. to provide a new and improved transmission line structure for conveying high frequency Waves covering a relatively wide range of frequencies.

It is another object of my invention-to provide a new and improved high frequency 1transmission line which may be easily adjusted for reflectionless-transmission of Waves thereover.

It is stillanother object of my invention to provide a newand improved high frequency transmission line which is simple to construct, inA which the energy loss is reduced and in which the corresponding cost due to insulating material is reduced.

Such a line necessarily employs insulators; for maintaining the inner and. outer conductors in spaced relation. Furthermore, for Wide band transmission the number of insulators employed is often greater than that required for mechanical considerations. That is, each insulator introduces theline that suiiciently reflectionless transmis sion of energy over the line is effected.

The features of my invention which I believe tobe novel are set forth with particularity in theappended. claims. My invention itself, howvantages thereof, may best be understoodl by reference to the following description taken in connection with theY accompanying drawing.V in

2. which Figs.` 1; 2, and,31represent'three different embodiments of myzinvention.

In Fig. 1 there isshown a coaxial cable having a .center'conductor lfof uniform'cross section and a tubularouter conductor 2 coaxial with conduetor`V l and of uniformV outside diameter; Insulating disks 3fofany suitable insulating material :are provided for.fmaintaining the conductor I centrally disposed: within the .tubular conductor 2. Theinsulators sarev` centrally perforated to receive the conductor* I'snugly and are of such size asV to t' close-ly" Within the conductor 2'. Moreover, thespacing between the insulators 3 is-that required because of mechanic-al considerations;- namely, supporting the conductor l within the conductor 2.

It isvvell known that, when insulating disks such" as`those-'shown in Fig. 1 are spaced uniformly within ya :coaxial cable, reection of transmitter energy-occurs- It has been found, furthermore, that if reilectingv points spaced at equal spacings.- throughout theV entire transmission line' systemfare provided with sufciently short spacings between adjacent points, each point'reflectingequal amounts of energy, broad-band'transmission :of energy is. effected. As is' well"known, this vcondition occurswhen the spacing between adjacent:reecting'points'is a very small 'frac` tioni of a wavelength' at the highest frequency Which'itfis desired to transmit; The smaller the spacing,- themore closely the line approaches a continuous-dielectric line and the wider the band of frequencies whichcan'be transmitted without-excessive standing-Wave ratio. Accordingly, there is provided in the transmission line of Fig. 1 aplurality of collars or sleeve members 4 formed of any suitablefconductingf:material, such as for examplecopper; The-members 4 may be attached to the inner conductor l in any suitable manner similarfto'thatrused for theinsulators, such as by crimpinggior-by means of set screws 5.

Fig. 2-i1lustrates a modification of my improved ransmission line in which the reection points spaced .between the insulators 3 comprisecollar or sleeve members S'whichare attached to the outer kconductor 2 in any' suitable manner, such as byfcrin'iping'ory the setscrewsv 'I to reduce the inner diameter of the outerI conductor at these points. Moreover; the-outer conductor 2 preferably; is formedinto short sections which are joined togetherI by any suitable means, such as the threaded coupling :member 8.

Still-fanothermodification of my invention isv ilh-istratedV in Fig, 3, in which; intermediate the i insulators 3, ,thererarezemployed' both the' sleeve il attached to the inner conductor l and the sleeves 6 attached to the outer conductor 2. The sleeves l and may be aligned transversely of the transmission line, as shown, or they may be staggered to provide proper reflections.

In the operation of the transmission line disclosed, the sleeve members 4 and 6 serve as capacitive reflection points along the transmission line which are so spaced with respect to the insulators 3, in correlation with the frequency of the energy transmitted over the transmission line, that each sleeve serves to behave like the insulator which it replaces. In the construction of Fig. 3, as well as the other constructions of course, the spacing between the reective sleeve and the opposite conductor is limited so that the spacing between adjacent conductive surfaces is such that voltage flash-over does not occur.

An important advantage of my improved transmission line is the decrease in power loss over the conventional transmission line employing insulators instead of the reflective members 4 or 6. It has been found that, in a transmission line of the conventional type, when large conductors are used the losses due to the presence of the spaced insulators amount to approximately onethird of the total energy loss of the line. However, by the use of thaJ metal capacitive reectors 4 or 6, these losses are reduced in proportion to the number of actual insulators used, since the capactitive reflectors or 6 introduce negligible energy loss. Thus, in a line employing my invention as described above, with three out of every four insulators replaced by the sleeves 4, the insulator loss is reduced by '75 per cent and the total losses on the line, by about 25 per cent. Another advantage of my invention is the great reduction in cost of a transmission line for high frequency energy. In lines for transmitting high frequency energy of greater amounts of power, very large outer conductors of the order of three or six inches are required. In such lines, the cost of the insulators forms a large portion of the total cost of the line. Thus, for example, an insulator for a three-inch line costs approximately thirty-live cents, while an insulator for a six-inch line costs in the order of one and onehalf dollars. Bv my improved construction. '75 per cent of the total insulator cost may be eliminated. thus considerably reducing both the initial cost and subsequent operating costs of transmission lines.

While I have shown particular embodiments of my invention, it will of course be understood that I do not wish to be limited thereto since modifications may be made and I aim by the appended claims to cover any such modifications as fall within the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the United States is:

l. A coaxial transmission line adapted for operation over a wide band of high frequencies comprising a tubular outer conductor and an inner conductor, a plurality of insulators spaced at regulator intervals throughout said line, said insulators providing a plurality of reflection points each causing reflection of the same amount of energy and also causing an undesired energy loss at said frequencies, the spacing between adjacent insulators being adequate for mechanical support of said inner conductor but substantially greater than that which provides sufficiently reectionless transmission for operation over said wide band, and a plurality of discrete short sections of said line regularly interspersed with said insulators each providing substantially reduced spacing between said conductors, each of said sections being arranged to provide an additional reflection of the same amount of energy as each insulator but negligible energy loss, the distance between adjacent reflection points throughout said line being short enough to provide sufficiently reflectionless transmission for operation over said wide band.

2. A coaxial transmission line adapted for operation over a wide band of high frequencies comprising a tubular outer conductor and an inner conductor, a plurality of insulators spaced at regular intervals throughout said line, said insulators providing a plurality of reflection points eachcausing reflection of the same amount of energy and also causing an undesired energy loss at said frequencies, the spacing between adjacent insulators being adequate for mechanical support of said inner conductor but substantially greater than that which provides sufficiently reiiectionless transmission for operation over said wide band, and a plurality of short metallic collar members carried by one of said conductors and regularly interspersed with said insulators, said members being arranged to provide additional reflection points each of which causes reflection of the same amount of energy as each of said insulators but with negligible energy loss, the distance between adjacent reflection points throughout said line being short enough to provide suiiiciently reiiectionless transmission for operation over said Wide band.

3. A coaxial transmission line adapted for operation over a wide band of high frequencies comprising a tubular outer conductor and an inner conductor, a plurality of insulators spaced at regular intervals throughout said line, said insulators providing a plurality of reflection points each causing reflection of the same amount of energy and also causing an undesired energy loss at said frequencies, the spacing between adjacent insulators being adequate for mechanical support of said inner conductor but substantially greater than that 'which provides suiciently reectionless transmission for operation over said wide band, and a plurality of short metallic collar members carried by one of said conductors and regularly spaced between each pair of adjacent insulators, said members being arranged to provide a plurality of additional reection points between adjacent insulators each causing reection of substantially the same energy as each of said insulators but negligible energy loss, the distance between adjacent reflection points throughout said line being short enough to provide suiiiciently reectionless transmission for operation over said wide band.

4. A coaxial transmission line adapted for operation over a wide band of high frequencies comprising a tubular outer conductor and an inner conductor, a plurality of insulators spaced at regular intervals throughout said line, said insulators providing a plurality of reflection points each causing reflection of the same amount of energy and also causing an undesired energy loss at said frequencies, the spacing between adjacent insulators being adequate for mechanical support of said inner conductor but substantially greater than that which provides sufficiently reiiectionless transmission for operation over said wide band, and a plurality of pairs of short metallic collar members regularly interspersed with said insulators, one member of each pair being The following ref REFERENCES CITED me of this patent:

UNITED STATES PATENTS Number short enough to provide sufficiently reflectionless 10 408345 transmission for operation over said wide band.

MARVEL W. SCHELDORF.

eremlces are of record in the Name Date Green Feb. 4, 1936 Tonks et a1 Sept. 17, 1946 Espley Oct. 8, 1946 Certificate of Correction Patent N o. 2,473,262.

read capacitive; line 66, for the Word regu- THOMAS F. MURPHY,

Assistant 'ommz'sszoner of Patents. 

